Chapter 2 SHOGKERS uper biters are amazing, for sure. But did you know that one of the most deadly fish on the planet doesn’t have any teeth at all? The electric eel has a special superpower for killing its prey— electricity! These fish have electrical organs that can send out pulses of electricity. Those pulses have enough power to stun, and perhaps even kill, a full-grown man. 49
50 I had a chance to fish for electric eels in some of the rivers that feed into the Amazon. And it’s one of the scariest fish I’ve ever encountered! Electric eel are widespread in South America, and you can never be sure where one will turn up! They live in rivers, lakes, small ponds, streams, and stagnant backwaters. They often hide in underwater caves or among underwater tree branches, roots, or logs. And that’s what makes looking for them so scary. No matter where I was, I knew that somewhere in the dark water an electric eel could be hiding. And if I happened to get too close—ZAP! This is what happened to our cameraman, Colm Whelan (sounds like COMB wee-lan), when we were filming
one day. We were wading in waistdeep water. All of a sudden, we saw Colm slump into the water. We rushed to help him. He was stunned and confused. It took us a few seconds to realize what had happened. Colm had accidentally brushed up against an electric eel. None of us actually saw the eel, but the effects were clear. That shock was strong enough to knock over a full-grown man. The electric eel may have a classic eel body shape, but it’s not really a true eel. It’s the largest member of a family of fish called South American knifefish. These fish can grow up to eight feet (2.4 m) long.
The electric eel’s jolt is much more powerful than that of any of its smaller knifefish relatives. But all electric fish are able to generate a weak electric field around their bodies. They use their electric field to communicate with each other. They also use it to find their way around or to find food in their dark, murky environment. An electric eel sends out its supershocking full-power pulses when it is hunting or when it feels threatened. Most of the time, an eel swims slowly, sending out small pulses of electricity. The pulses bounce, or echo, off objects in its environment. By sensing the echoes, the eel can tell how far away and how big those objects are.
‘(American|Paddlefish™ The American paddlefish lives in the Missouri and Mississippi Rivers. This may be one of the weirdest-looking fish in the world. It’s famous for its huge spatulashape snout. Paddlefish don’t send out shocks like electric eels. But its snout is lined with detectors that can pick up the electrical signals other animals give off. So paddlefish can use their super-sensitive snouts to find prey as they swim through dark, muddy water.
When the eel detects a fish that’s just the right size to eat, it slowly moves toward it. When it gets close enough, it blasts the fish with a pulse of electricity. For the fish, it must be like getting hit with a bolt of lightning! The stunned fish can’t even move. The eel opens its mouth quickly, sucks the fish in, and swallows it whole. My friend Dr. Will Crampton is an electric eel expert. Dr. Will said that a shock from an electrical outlet in your house is 110 volts. That’s nothing compared to the shock that an eel can give! Dr. Will said an average eel can produce a shock of more than 700 volts. Some people have said that even large horses have been stunned and killed by eel shocks.
When studying electric eels, our goal was to measure them and find out if bigger eels were stronger shockers than smaller ones. To do that, we were going to have to Benjamin Franklin and other scientists of hold them in our hands. the 18th century actually catch some and We were definitely learned some of their first lessons about electricity from protective covering. So, electric fish. going to need some we put on funny-looking rubber overalls and gloves. Rubber doesn’t conduct electricity. I just hoped it would be thick enough to shield us from the shocks! In order to find the eels, we used an electricity-detecting device. We waded into the water and dipped the device in wherever we thought eels might be.
The device made sound—click, click, click, click, click—whenever it picked up an eel’s electric field. Once we knew eels were in the area, we set traps for them at night. When we returned the next morning, we discovered we’d caught a few. The smallest was two feet (0.6 m) long, and the largest was more than four feet (1.2 m). They would give us a good comparison of size and power. Dr. Will had a special voltage detector called an oscilloscope (sounds like uh-SILuh-skohp) to measure the eels’ power. In some ways, an eel’s body is like a big 56
battery. We pressed one of the detector’s wires to the smaller eel’s head and the other wire to the end of its tail. When the eel pulsed, the device measured the result: 550 volts! About five times stronger than a typical electrical outlet! Could the bigger eel possibly be even more powerful? We attached the device. The big eel pulsed, and Dr. Will ee es mn normally insulates could hardly believe the them from their own attacks, but when wounded, they can 860 volts! That may be accidentally shock the highest voltage themselves! results. Its shock was anyone has recorded for any animal, anywhere in the world. That’s what I call a super shocker! 57
Chapter 3 SSG, an eT me ane ATT 0 TTT a é eal a lt mea You’ve probably learned about many birds and land animals that travel, or migrate, long distances. But most people don’t know that some types of fish migrate, too. These are the super swimmers! They travel incredibly long distances. And to get where they’re going, they swim through some dramatically different habitats. 59
Unlike the electric eel, the New Zealand longfin eel is a true eel. It makes one of the most impressive migrations of any animal on the planet. It’s New Zealand’s biggest and longest-lived freshwater fish. The largest of them reach lengths of seven feet (2 m) and can weigh more than 50 pounds (23 kg). The longfin eel is born far out in the Pacific Ocean. Almost as soon as they’re born, the babies, or larvae (sounds like LAHR-vay), begin a long journey. They drift on ocean currents for more than a thousand miles (1,600 km), finally reaching the freshwater rivers and streams of New Zealand. Once they get there, the larvae grow and develop into strong swimmers called
i 2 elvers. They can battle Did You Know? One female longfin eel can produce steepest waterfalls. So, between 1 million and 20 million eggs. The eggs need to they can be found far be fertilized by a male upstream. Even in fast- eel. But no one knows yet exactly how that happens! their way up even the it’s not surprising that moving creeks and in high mountain lakes! One of the most amazing experiences that I’ve had with eels was on the South Island of New Zealand, in a beautiful mountain lake called Lake Rotoiti (sounds like row-toe-EE-tee). This lake is famous for its monster-size eels. And I had a chance to go scuba diving with them! At first I was a little afraid because I’d heard a story of eels chasing divers and biting fishermen. But as soon as I got in the 61
water with them, I knew those stories were exaggerated (sounds like ig-ZAJ-uh-rey-tid). The eels were more curious than aggressive. They swam all around me. They seemed to be looking and smelling for something to eat. But lucky for me, they didn’t view me as food. I was able to spend almost an hour underwater with them. I was as curious about them as they were about me. But every time I tried to get a hold of one, it slipped right out of my hands. Have you ever heard the phrase “as slippery as an eel”? It’s not because they’re devious (sounds like DEE-vee-uhs). It’s because they are impossible to hold on to! Their bodies are covered in slimy mucus, which helps them wriggle safely over land
when they need to cross from one lake or stream to another. Longfin eels are not just super swimmers, they are super travelers! And they are super survivors, too. I was amazed to find out that some of the eels in Lake Rotoiti were more than 100 years old! Longfin eels make their home in freshwater for nearly all of their adult lives. But when they reach the end of their life span, they must swim back to the place where they were born. Imagine: 100-yearold eels making their way out into the open ocean again. Once more, they will take the thousand-mile (1,600-km) journey—this time in reverse. When they reach their birth spot, they’ll spawn, or lay their eggs. The old eels will die. And soon a new generation of longfin eels will be born.
Believe it or not, jaguars aren't -~ the most common large predators in the Amazon River area. Huge, super-swimming catfish hold that title! The biggest of these is the piraiba (sounds like par-UH-ee-buh). It's one of South America’s largest freshwater fish. It can grow to more than
goliath catfish - eight feet (2.4 m) in length and weigh more than 300 pounds [136 kg). Piraiba make epic migrations up and down the Amazon. During the breeding season, they can swim more than 2,000 miles (3,219 km), from the mouth of the Amazon in Brazil to the river’s remote headwaters in Colombia, Ecuador, and Peru.
One of the world’s most famous super swimmers has a life cycle that is almost the exact opposite of the longfin eel’s. It is the Chinook (sounds like shi- NOOK) salmon—the biggest type of Pacific salmon. The largest can grow to almost five feet (1.5 m) in length and weigh more than 100 pounds (45 kg). Chinook are born in freshwater streams—often far inland or on high mountain slopes. Then they migrate out to the ocean, where they spend their adult lives. At the end of their lives, they migrate back to freshwater to spawn, and then 66
they die. This whole process usually takes only three to seven years. But during that time, the fish may swim all along the Pacific coast of North America. The rivers of the Pacific Northwest used to run red at certain times of the year. That’s because when Chinook salmon are ready to spawn, they turn bright red. Hundreds of them begin to swim upriver at the same time. Often these fish are so large that their backs stick out of the water! These salmon can travel as far inland as Idaho, Montana, and the interior of Alaska. Sadly, today there aren’t nearly as many salmon as there once were. Dams have blocked their migrations in some areas. This has made it difficult for adult fish to reach their spawning grounds.
Many rivers that haven’t been dammed, such as the Kenai (sounds like KEE-nye) River on the Kenai Peninsula in Alaska, still have strong salmon runs. The Kenai is famous for its enormous super swimmers. Many of the record-breaking, nearly 100-pound (45-kg) Chinook salmon have been caught there. That’s huge, even for the largest of all the Pacific salmon! White sturgeon (sounds like STURjuhn) is another giant fish that lives most of its life off the coast of the Pacific Northwest. Like Chinook salmon, they are super swimmers that are born in freshwater but spend most of their lives at sea. Unlike salmon, though, they don’t die after they spawn. They make the voyage from ocean to river year after year.
And sturgeon aren’t only super swimmers. Like longfin eels, they are also super survivors! White sturgeon have been on Earth for about 100 million years. And individuals have been known to live for more than 100 years. That means there could be some super swimmers still alive today that were born in the early 1900s. That would be about the same time the Wright brothers were making their historic first flights! But today, even these super survivors are in danger of going extinct because of human activities. Try to find out all you can about the rivers, streams, and lakes in your local area. The super swimmers that live there need your help and protection!
Zeb Hogan captures and \\ IR tags a giant stingray. i
Chapter 1 » hile I was in Thailand - tagging giant catfish, I heard tales of huge stingrays. They were living not in the ocean but in the freshwater of the Mekong River. I’d never heard of a stingray in freshwater. But if any of the stories were true, the giant freshwater stingray must be a monster! It would far outweigh even the record-breaking giant catfish.
Some people said they’d seen stingrays that were more than 10 feet (3 m) wide and 20 feet (6 m) long. The stingrays I had seen in the wild were much smaller than that. I wanted to find one of these legendary giants. But I wasn’t sure where to begin looking. Biologists weren’t even sure how many might still be alive in the wild. One of the more interesting stories I had heard was about an older man in the town of Nakorn Sawan (sounds like NA-korn sah-WAN). People said that 15 years ago, this man caught a giant stingray so big that it took a dozen men to haul it out of the water. It barely fit in the back of a huge dump truck. I wondered what it must have been like to come face-to-face with a giant like this.
Ancient Greek dentists I wanted to talk to the used the venom from the stingray’s spine as man to find out more. an anesthetic. I knew just where to start: with my friend Dr. Chavalit Vidthayanon (sounds like cha-vah-LET VID-thy-a-non). He’s a freshwater fish biologist from Thailand. Sure enough, Dr. Chavalit helped me get in touch with the older man. As the three of us sat together outside the man’s house, the man told me how he had hooked the big stingray. It took him and a partner 11 hours to reel it in! He told me the fish weighed 485 kilograms. That would be more than 1,000 pounds! If this man’s story was true, the giant freshwater stingray could be the world’s largest freshwater fish.
slype siofjRa ys 76
I wanted to believe this man, but I couldn’t be sure. In my experience, fishermen love to exaggerate the size of the fish they catch. So unless I see a fish for myself, I’m always a little skeptical (sounds like SKEP-ti-kuhl). It’s one thing to hear a story about a huge fish, but it’s quite another to see it with my own eyes! As a scientist, I want to compare people’s stories with evidence, measurements, and facts. Without the facts, it’s hard to know what’s true and what’s make-believe. Especially with fish that grow to what sounds like mythical size! I went back to my work with giant catfish. But the man’s story kept running through my mind. I told Dr. Chavalit and others that if anyone caught a giant stingray, I wanted to
hear about it. Many months went by with no news. Then, finally, the phone rang. Someone had caught a stingray that was 14 feet (4.2 m) long! This I had to see! The stingray had been caught in the Mekong River, near the CambodiaVietnam border. I rushed there to see it. Stingrays are close relatives of sharks. Sometimes people call them pancake sharks. That’s because they look a little like sharks that have been flattened. Like sharks, stingrays have skeletons made of cartilage (sounds like KAHR-tuhlij) rather than bone. But stingrays don’t have sharp, pointed teeth like sharks do. Their mouths are on the underside of their bodies. And instead of teeth, they have hard, flat pads that help them crush their prey.
Special sensors in their snouts help them detect their favorites—shrimp, clams, and small fish—even in dark, muddy water. Stingrays spend most of their time on the river bottom. Their eyes sit on top of their heads, so they can look around while they are hiding in the mud. Stingrays are not aggressive like some sharks are. But they do have a secret weapon: Attached to the base of their tail is a long stinging spine. A stingray will only strike if it’s frightened or if it feels threatened. But that spine is razorsharp. And it’s coated with venomous mucus. That spine is also strong enough to pierce bone! 79
I wasn’t sure what to expect when I reached the newly captured giant stingray. Would it really be as big as they said it was? I hoped so, but I didn’t want to be disappointed. I tried not to get too excited. What I saw, however, stunned me. It was by far the biggest stingray I had ever seen in the wild. It wasn’t as big as the one the old man said he caught. But seeing this one made me think that even bigger giant stingrays must be out there. No way could this stingray be the only giant in the river! It was time to find out much more about these mysterious monsters! Scientists have only been studying this fish closely for the past 20 years or so. 80
There’s so much more we want to know. Yet giant stingrays are disappearing fast. Overfishing, pollution, and loss of habitat have greatly reduced their numbers in some areas. In Thailand, along one river, many stingrays have been reported floating dead after chemical spills. I hoped that maybe in our search for a record breaker, we would discover the special areas that giant stingrays prefer. I knew we needed to find out all we could about these amazing creatures soon. We also needed to figure out how to protect them. We needed to figure out where to create protected areas for them to live in before they were all gone. I had finally found one giant freshwater stingray. But how was I going to find others?
Quite a catch! A local man steadies a giant stingray by the tail while Zeb Hogan adjusts the tarp under it.
traveled up and down the Mekong River in my quest to find giant stingrays. It wasn’t easy. These fish live in a murky world that is strange and unfamiliar to us. I started my search in the local fish markets. I’d visit the markets early in the morning. That’s when the vendors would put fresh fish out for sale on trays or large banana leaves.
Most vendors sold catfish or carp, but every once in a while I’d see someone selling stingray. Usually the ray would be cut in pieces, so I couldn’t tell how big it was when it was alive. I’d ask the vendors where the fish came from. And they’d tell me the name of a small village along the river. Traveling by boat, I then visited the small villages where stingrays had been caught. ’'d park my boat on the riverbank and walk up to the nearby houses. I’d ask whoever I saw if they knew of anyone who caught stingrays. In these little towns, everyone knows one another. Everyone knows who farms and who fishes—and especially who fishes for stingray. The stingray fishermen were very talented. Stingrays don’t swim into
nets, and the everyday rods and reels most fishers use are just not strong enough to land them. Catching stingrays takes special skill and equipment. After a long search, I finally found one man who knew where and how to catch them. He told me that he liked to fish in shallow sandy areas where stingrays look for food at night. Instead of fishing line, the man said he used rope, huge hooks, and a 10-pound (4.5-kg) fish as bait. He attached a large rock to the rope to keep the bait on the bottom. Then he tied everything to a floating barrel. He said he left his baited hook in the river overnight. Then he looked for the floating barrel in the morning. Many nights, a stingray would eat all the
bait and then try to leave, pulling the rock and barrel behind it all over the river. I fished with the man for a couple of nights, but we had no luck catching a big one. And I was afraid his way of fishing might exhaust and even hurt the fish if we did catch one. I didn’t want that to happen. At this time, I was searching on a remote stretch of the Mekong, where the villages were small and far apart. I kept asking people if they knew about recent catches. But more often than not, by the time I heard about a catch, the stingray would already have gone to market. I was always too late! I knew it was time to find another location. Just by luck, I heard about another area where people were catching
rays. To my surprise, it was near a major city! When I got to the city, I joined my friend Rick Humphries and his expert fishing team. If anyone could land a giant, it would be Rick. And I knew that he and his team use special hooks that are not as likely to hurt the fish. They also use heavy-duty gear that helps bring a fish in quickly without exhausting it. If we did catch a giant, I wanted to be ready to weigh and measure it. So, first I pumped up a large plastic swimming pool and filled it with water from the river. The pool was 10 feet (3 m) wide—big enough to safely hold a giant while we measured tt. 87
88 Next, I set up a special | . canvas sling to | hold and support 7 7 the fish. We would ae slip the fish carefully into the sling. Then we would hang the sling from a large scale to see how much it weighed. To be sure it was safe, I tested the sling on myself! It was strong enough to weigh me, so I figured it would be sturdy enough for even the biggest fish. It didn’t take long before one of Rick’s team members had hooked a big one. Of course, the fish took the bait and then immediately buried itself in the mud on the bottom of the river!
Bringing the fish up was going to take patience and strength. The fisher who caught it said it was like hooking a submarine! No matter how strong you are or how sturdy your gear, it’s hard to get such a wide, flat fish out of the mud and up to the surface. After a lot of effort, we finally had it up near the boat. That’s when everyone had to be especially careful. We gently and carefully tied the stingray’s stinger flat against its tail with a long strip of cloth. Now the stingray could swing its whiplike tail freely, but we would all be safe. Once its barb was secured, we put the stingray in a soft net, hauled it to shore, then placed it in the pool. This was the first of several we were able to catch, weigh, and measure.
The largest stingray we caught in that area was a female. From snout to tail, she was more than nine and a half feet (3 m) long. She weighed 365 pounds (166 kg). She was a beautiful, healthy fish, but not nearly as big as the monster the old man had described. As we released her back into the river, we wondered if we'd ever find a larger one in the Mekong. Rick told me he had had some luck getting bigger stingrays in western Thailand, on a wild and remote section of the Maeklong (sounds like MAY-klong) River. We headed there next.
alta be aaa e hrcas il A adCeek el aatte Ss eae Ne Sa re ate - brutal! Piranhas often ate our baits. The we finally caught and tagged a 400-pound Believe it or not, there are dozens of species of freshwater stingray! Most of them live in the rivers of South America. In 2015, my team and | went to Argentina to look for the largest of them—the short-tailed river ray. We explored deep pools, swiftly flowing rapids, shallow sandy banks, and still backwaters. The conditions were days were hot and sunny. Sudden storms would drench us. At night, we were eaten alive by mosquitos. After a lot of effort, (181-kg) river ray! ©
Chapter 3 _ wanted to be prepared to tag x any giants we might be lucky = enough to catch in the Maeklong. I planned to use tags that would transmit electronic signals underwater. Each tag held a microchip that would give each fish its own identification number. No one had tried anything like this before. I wanted to make sure we got it right.
The plan was to place underwater receivers six miles (10 km) apart along a stretch of the river. The receivers would record the movements of the tagged fish. I asked fish veterinarian and stingray expert Dr. Nantarika Chansue (sounds like nahn-tah-REEK-ah CHAN-soo) for help with my plan. We went to the local fish market and bought a small stingray to practice on. The transmitters would have to be inserted under the stingrays’ skin. Dr. Nantarika figured out a way to place the transmitters that would not hurt the fish. Now we were ready to catch a Stingrays are fish! There are around giant! And soon, 200 different Rick had one stingray gray species. sp hooked. His fishing
pole bent down sharply toward the water’s surface as he struggled to bring the fish up. Then suddenly—SNAP! The hook broke, sending Rick tumbling backward. We knew this must have been a huge fish. That hook was made to hold 500 pounds (227 kg)! We were all disappointed to lose that big one. But soon we had another on the line. This one was a young adult and not as big. Still, it would be great to tag this youngster and be able to observe him as he grew up. We eased him out of the water and into the pool. Dr. Nantarika placed the transmitter under the stingray’s skin near its tail. We were relieved to see that he didn’t seem to mind the procedure. We had him back in the river within minutes.
We were determined to catch a fullgrown adult next. So, Rick and his team got back to work. Later that day, I got a call. Rick said they had a big one on the line. I rushed down to the water to help. Yes! This was the giant we’d been hoping for. It was almost twice the size of the largest stingray we’d caught in the Mekong. It took 12 men to get it out of the water and into the pool. Right away, Dr. Nantarika knew the fish was a female. And, even better, she was pregnant! Using a portable ultrasound machine, Dr. Nantarika could see three babies inside. This was incredible news! It meant that there was a healthy breeding population of giant stingrays in this area.
We successfully placed the transmitter under the stingray’s skin. I estimated that this fish must weigh more than 600 pounds (272 kg). I had to guess because the crane we needed to set up our scale was late arriving. We couldn’t risk keeping the stingray out of the river any longer while we waited. We eased her back into the water and watched as she swam back down into the murky depths. Two months after we successfully tagged these fish, I went back to the Maeklong. I pulled the first receiver from the water and connected it to my laptop. Once the data was downloaded, we could clearly see which rays had passed this spot and how many times they had done so. With this data and the data from